1. The Field of the Invention
The present invention relates to an apparatus for determining whether or not fog is present in an environment around a vehicle using images picked up by a camera mounted on the vehicle.
2. Description of the Related Art
There has been known an apparatus for executing an image processing on a picked up image of an on-vehicle camera for determining the presence of fog (as disclosed in, for instance, Japanese Patent No. 3444192). In Japanese Patent No. 344419, the presence of fog is determined based on a degree of image blurring. With fog being present, the image gets blurred. Thus, the presence of fog is determined upon the estimated degree of image blurring. In estimating the degree of image blurring, first, a differential calculus is executed for each pixel of an entire image to calculate a rate of change of brightness (the amount of edges) in each pixel of the image. The brightness variations are used to estimate the degree of image blurring.
With the apparatus disclosed in Japanese Patent No. 3444192, the result of determining the presence of fog is utilized in recognizing a white line on a road. In recognizing the white line on the road on which a vehicle is traveling based on an image picked up by the on-vehicle camera, if fog is present in an atmosphere on the road, the image gets blurred with a resultant difficulty of recognizing the white line. Therefore, the presence of fog is determined prior to recognizing the white line. It is also disclosed that if the presence of fog is determined, fog lamps are turned on.
An apparatus, disclosed in Japanese Patent No. 3312729, is not of a type that determines only the presence of fog. If an image gets blurred due to bad visibility caused by fog or the like, or, dirt on a windscreen of a vehicle, it becomes hard to appropriately monitor the vehicle exterior (i.e., a monitoring a distance between an own vehicle and an object at a distance from the vehicle, i.e, exterior of the vehicle). To address such an issue, the determination is made whether or not the image is blurred.
In the method of determining the image blurring disclosed in Japanese Patent No. 3312729, a representative value of the brightness variation of the image is calculated based on the brightness variations in a fixed portion of the image, wherein the fixed portion is set to an upper center section of the image. In more detail, the representative value of the brightness variation of the image is estimated based on a ratio of the number of pixels in which the brightness variation exceeds a predetermined threshold value.
Both the apparatuses, disclosed in Japanese Patent No. 3444192 and Japanese Patent No. 3312729, determine whether or not the image picked up by the on-vehicle camera gets blurred for thereby making a judgment on the presence of fog. If the brightness variations of each pixel of an entire image are calculated, an issue arises with an increase in processing time or load for carrying out the image processing as disclosed in Japanese Patent No. 3444192. Meanwhile, with the apparatus disclosed in Japanese Patent No. 3312729, the brightness variations of only the fixed area, set to the upper center section thereof, are calculated, resulting in a lower load or shorter processing time than that of the device disclosed in Japanese Patent No. 3444192. However, in image object in the image of a close range object to the own vehicle is relatively and clearly picked up even in the presence of fog. Therefore, if the object is picked up in the fixed area on the image at a close range from the vehicle, an issue arises with a difficulty of precisely determining the presence of fog.
With the above view in mind, the present applicant has made an invention on an apparatus, operative to determine the presence of fog using an image of a far-flung road region determined on the image picked up by an on-vehicle camera for representing a region over a road in a given far-flung distance from a vehicle, of which patent application was filed (Japanese Patent Laid-open publication No. 2006-349492). Thus, if the region of the image for which the presence of fog is determined is allocated to the region over the road, it is highly likely that due to the road normally continuing to a far-flung area, such a far-flung area involves a pickup image of a far-flung portion. This enables the presence of fog to be precisely determined.
Further, WO 03/069275 discloses means for determining whether or not fog is present in outside air, surrounding a field of view from a driver's seat and a vehicle, in an image picked up by an on-vehicle camera.
With such a method, a road portion and a sky portion are determined based on brightness in the image picked up by the on-vehicle camera. Thereafter, a calculation is executed to obtain coefficients of extinction in both areas under a Koschmieder's low, upon which the field of view is produced and the existence of or nonexistence of fog is determined based on the resulting coefficients of extinction.
However, with the apparatuses disclosed in Japanese Patent Laid-open publication No. 2006-349492 or WO 03/069275 for determining the presence of fog, it is likely that when picked up by the on-vehicle camera mounted on a vehicle running on a road passing through a forest like a mountain corridor, a far-flung road region is present in the forest and, therefore, underexposure phenomena occurs in the pickup image. If such underexposure phenomena are present in the far-flung road region, there is a possibility of determining in error that the image is enveloped in fog.
The present invention has been completed with a view to addressing such issues and has an object to ensure a precision in determining the presence of fog even if underexposure phenomena occur in a far-flung road region of an image.